This invention relates to a missile and particularly concerns a guide assembly therefor. The guide assembly includes vanes which have an inwardly pivoted, folded position of rest and an outwardly pivoted, deployed state which they assume in flight during which the missile rotates about its longitudinal axis.
Missiles which have foldable stabilizing guide assemblies and which, for example, by virtue of the position of the vanes, rotate about the longitudinal missile axis (compensating twist) during flight are well known. To obtain a defined position of the vanes along the entire flight path, in the known missiles the vanes are blocked (immobilized) by a locking device in their outwardly pivoted, deployed end position.
It is, among others, a disadvantage of the above-outlined guide assemblies that during flight the forces exerted on the vanes lead to varying mechanical stresses to which the vane locking mechanisms are exposed. Such changing mechanical stresses often result in jars and vibrations to the entire missile which, for example, when sound sensors are used, may lead to a defective operation of fuzes of high-explosive projectiles.
Further, in a known projectile fin assembly, as described in United States Statutory Invention Registration No. H905, the center of gravity of each vane (fin) is, in the folded state of the vane, situated inward of the pivotal axis of the vane; That is, the center of gravity of each vane is at a smaller distance from the longitudinal axis of the missile than the pivotal axis of the respective vane. Further, the maximum angle that the vanes may assume in their deployed end position is generally about 90xc2x0. It is a disadvantage of such a construction that, in flight, a state of equilibrium in the deployed position is not readily assumed and it may even occur that in some angular ranges the vanes pivot toward the folded position. Also, because of undefined angular magnitudes and undefined abutment positions, undesired impacting by the vanes may occur with disadvantageous effects, for example, on the fuze.
It is an object of the invention to provide an improved missile guide assembly of the above-outlined type whose vanes assume in the deployed state an aerodynamically favorable position without the forces exerted thereon (forces derived from air streams, centrifugal forces and mass inertia of the vanes) causing jars of the missile.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the missile includes a missile body and a guide assembly mounted on the missile body. The guide assembly has a plurality of pivots and a plurality of vanes mounted on respective pivots for a swinging motion between a folded position of rest and a deployed flight position. The vanes are arranged for free pivotal motion during flight in response to forces acting thereon to determine the flight position. In the folded position of each vane, its center of gravity is situated at a greater distance from the longitudinal axis of the missile body than the pivotal axis of the respective vanes. Abutments limit the flight position of the vanes to a maximum angle defined between the length dimension of the vanes and the longitudinal axis of the missile body. The maximum angle is greater than 90xc2x0.
The invention is based essentially on the principle to provide a determined, but unblocked (that is, not locked or immobilized) deployed state of the vanes during flight, and to locate the center of gravity of each vane such that in the folded position of the vanes the center of gravity is farther away from the longitudinal missile axis than the pivotal axis of the vanes. Thus, the vanes, after the missile leaves the weapon tube, are pressed by the initially very high opposing air stream forces into a rearward end position defined by an abutment and subsequently, the vanes are pivoted forward into a frontal end position which is determined by an equilibrium of the forces affecting the vanes during flight. In the state of equilibrium the forces derived from the air stream push the vanes rearwardly while the mass inertia forces pull the vanes forwardly since the remainder of the missile is braked to a significantly greater extent than the vanes. In any event, the forces derived from the air streams are generally greater than the mass inertia forces, but as a rotation of the missile about its longitudinal axis starts, centrifugal forces generate a torque which also effects a forward pivotal motion of the vanes. Although the centrifugal force continuously increases during the flight of the missile, its axial component decreases as the vanes pivot forward. As a result, a torque equilibrium occurs where the angle xcex1 representing the angle between the length dimension of the vane and the longitudinal axis of the missile is generally greater than 90xc2x0.
The jars which may be caused by the impact of the vanes on their respective abutment do not lead to an unintended fuze activation because the fuze is armed only when the missile is at a certain distance from the firing device (muzzle area safety).